Glass encapsulated reed switches are well known in the art. Present day commercial reed switches typically comprise two metal reed members and a short length of glass tubing. The reed members are approximately flat and are positioned within the glass tubing in an overlapping arrangement and have a slight offset. The glass tubing can be, for example, cylindrical or oval in cross section and is sealed directly to the ends of the metal reed members by flowing the glass locally to seal sections of the reed elements.
Reed switch configuration as well as construction techniques for assembling reed switches have been extensively developed. The prior art contains numerous examples of these techniques and includes U.S. Pat. Nos. 3,794,944, 3,866,317, 3,938,066 and 4,055,888.
The reed switches of the prior art are further characterized by a pair of glass-to-metal seals formed where the metal reed elements exit the glass envelope. Known methods for forming the required seals include those taught in U.S. Pat. No. 3,660,064. Disclosed therein is a method of construction using infrared absorbing glass envelopes which receive a pair of metal reeds at opposite open ends thereof. To form a seal, infrared radiation is applied to the ends of the envelope. The glass at the ends of the tube partially melts and flows onto the metal reeds. Only a limited portion of the glass envelope must be heated above the glass softening temperature. Apparatus disclosed in U.S. Pat. No. 3,518,411 provides means for limiting the temperature rise in the glass envelope to only the end regions of the switch.
Technology for sealing metal-to-glass in other applications has also been developed, typically for sealing metal caps to glass envelopes. U.S. Pat. No. 4,509,880 discloses a metal-glass seal characterized by a thin, multicomponent metalized layer on a glass member inserted within a tubular metal sleeve. The seal is formed by flowing tin solder in the residual gap while the glass remains unsoftened. U.S. Pat. No. 3,932,227 discloses a metal cap-to-glass envelope seal characterized by several layers of multicomponent alloys deposited on both mating surfaces. A hermetic seal is formed therebetween by compression techniques. Other examples of multicomponent, multilayer alloys used in sealing structures such as anode caps to television picture tubes, or the like, include U.S. Pat. Nos. 3,929,470, 3,803,875, 3,948,615, and 4,002,506.
U.S. Pat. No. 3,646,405 discloses a method and apparatus for providing a hermetic seal between an insulator and metal terminals. A metal lead passing into a glass envelope is sealed using a configuration which includes a titanium disc affixed to a glass annular ring at the base of the glass envelope. The metal lead is initially coated with multilayered alloys, passed through the titanium ring and is soldered thereto.
The prior art also includes U.S. Pat. No. 4,236,045 which discloses an electrical lamp wherein a filament passes into a glass envelope. A glass-to-metal seal is accomplished by a metal plug comprised of tin or lead and a second metal such as titanium. To form the seal, the metal plug is positioned at the end of the glass envelope and is heated by conventional techniques above the melting point of the solder, without softening the glass.
U.S. Pat. No. 3,959,682 discloses a hermetically sealed glass lamp provided with a current lead sealed to a lamp envelope using a primarily molybdenum foil and welding agent consisting primarily of steel and iron. The hermetic seal is accomplished by conventional spot welding techniques.
A popular technique used in the past to fabricate reed switches involves the addition of oxygen in the region where the glass to metal seal is to be effected to form an "oxide seal". However, this technique is less than perfect since it is necessary to eliminate oxygen from inside the sealed reed switch tubing in order to prevent oxidation of the electrical contact points formed by the reed elements. The introduction of oxygen into the manufacturing environment that would, ideally, be oxygen free, has been a problem in prior art fabrication techniques.
It would be advantageous to provide an improved reed switch and method for making such a switch wherein the bond between the glass tubing and the metal reed switch leads is enhanced, without the need to use an oxide seal, to provide an extremely strong and rugged seal that will withstand the external forces applied to the metal leads when the reed switch is in use. The present invention provides such an improved reed switch and method.